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Transcript
No homework for Wednesday Read Chapter 8! Next quiz: Monday, October 24 1 Monday, October 24, 2011 Chapter 7 Atoms and Starlight Monday, October 24, 2011 Types of Spectra: Pictorial Some light sources are comprised of all colors (white light). Other light sources contain just a few colors. Some are missing just a few colors. 3 Monday, October 24, 2011 Emission Spectrum: Graphical 4 Monday, October 24, 2011 Absorption Spectrum: Graphical Absorption lines 5 Monday, October 24, 2011 Atomic Structure • An atom consists of an atomic nucleus (protons and neutrons) and a cloud of electrons surrounding it. • Almost all of the mass is contained in the nucleus, while almost all of the space is occupied by the electron cloud. Monday, October 24, 2011 Grapeseed in the middle of 4.5 football fields! Electron Orbits • Electron orbits in the electron cloud are restricted to very specific radii and energies. • These characteristic electron energies are different for each individual element. Monday, October 24, 2011 Electron Orbits • Electron orbits in the electron cloud are restricted to very specific radii and energies. r1 , E 1 • These characteristic electron energies are different for each individual element. Monday, October 24, 2011 Electron Orbits • Electron orbits in the electron cloud are restricted to very specific radii and energies. r2 , E 2 r1 , E 1 • These characteristic electron energies are different for each individual element. Monday, October 24, 2011 Electron Orbits • Electron orbits in the electron cloud are restricted to very specific radii and energies. r3 , E 3 r2 , E 2 r1 , E 1 • These characteristic electron energies are different for each individual element. Monday, October 24, 2011 Atomic Transitions • An electron can be kicked into a Eph = E3 – E1 higher orbit when it absorbs a photon with exactly the right energy. • The photon is absorbed, and the electron is in an excited state. Eph = E4 – E1 Wrong energy (Remember that Eph = h*f) • All other photons pass by the atom unabsorbed. Monday, October 24, 2011 Electron Orbits & Emission 9 Monday, October 24, 2011 Atomic Transitions Electrons spontaneously decay back down to “ground” state See animation at: http://astro.unl.edu/classaction/animations/light/hydrogenatom.html 10 Monday, October 24, 2011 Continuous 11 Monday, October 24, 2011 Emission 12 Monday, October 24, 2011 Absorption http://astro.unl.edu/classaction/animations/light/ threeviewsspectra.html 13 Monday, October 24, 2011 Kirchhoff’s Laws of Radiation (1) 1. A solid, liquid, or dense gas at non-zero temperature will radiate at all wavelengths and thus produce a continuous spectrum. Monday, October 24, 2011 Kirchhoff’s Laws of Radiation (2) 2. A low-density gas excited to emit light will do so at specific wavelengths and thus produce an emission spectrum. Light excites electrons in atoms to higher energy states Transition back to lower states emits light at specific frequencies Monday, October 24, 2011 Kirchhoff’s Laws of Radiation (3) 3. If light comprising a continuous spectrum passes through a cool, low-density gas, the result will be an absorption spectrum. Light excites electrons in atoms to higher energy states Frequencies corresponding to the transition energies are absorbed from the continuous spectrum. Monday, October 24, 2011 The Spectra of Stars Monday, October 24, 2011 The Spectra of Stars The inner, dense layers of a star produce a continuous (blackbody) spectrum. Monday, October 24, 2011 The Spectra of Stars The inner, dense layers of a star produce a continuous (blackbody) spectrum. Cooler surface layers absorb light at specific frequencies. Monday, October 24, 2011 The Spectra of Stars The inner, dense layers of a star produce a continuous (blackbody) spectrum. Cooler surface layers absorb light at specific frequencies. => Spectra of stars are absorption spectra. Monday, October 24, 2011 H He Ne Kr 18 Monday, October 24, 2011 Since pattern is unique for every element, the emission spectrum serves as an atomic fingerprint, telling us about the composition of celestial objects. H He Ne Kr 18 Monday, October 24, 2011 19 Monday, October 24, 2011 20 Monday, October 24, 2011 • The specific wavelengths seen in an emission line spectrum are due to • A) photons dropping to lower energy orbits. • B) photons jumping to higher energy orbits. • C) electrons dropping to lower energy orbits. 21 Monday, October 24, 2011 • Below is a model 3-level hydrogen atom. Each of the circles represents an energy level/ orbit around the nucleus, from the ground state (n = 1) to the second excited state (n= 3). The spacing of each circle is proportional to the energy of each orbit. The arrows represent electron transitions. Which transition will result in the emission of the longest wavelength photon? • A) A • • B) C) B C 22 Monday, October 24, 2011 1 2 3 Which transitions were responsible for each of these absorption lines? a) A: 1-2 B: 2-4 C: 1-4 b) A: 1-4 B: 2-4 C: 1-2 c) A: 4-1 B: 4-2 C: 2-1 23 Monday, October 24, 2011 4 Chapter 8 The Sun Monday, October 24, 2011 Guidepost In this chapter, you can use the interaction of light and matter to reveal the secrets of the sun. Because the sun is a typical star, what you are about to learn are the secrets of the stars. This chapter will help you answer three essential questions: • What do you see when you look at the sun? • How does the sun make its energy? • What causes sunspots and other forms of solar activity? The sun will give you a close-up look at a star. Monday, October 24, 2011 Outline I. The Solar Atmosphere A. The Photosphere B. The Chromosphere C. The Solar Corona D. Helioseismology II. Nuclear Fusion in the Sun III. Solar Activity Monday, October 24, 2011 Outline I. The Solar Atmosphere A. The Photosphere B. The Chromosphere C. The Solar Corona D. Helioseismology II. Nuclear Fusion in the Sun III. Solar Activity Monday, October 24, 2011 Today! General Properties • Average star Monday, October 24, 2011 General Properties • Average star • Spectral type G2 - O B A F G K M Monday, October 24, 2011 General Properties • Average star • Spectral type G2 - O B A F G K M • Only appears so bright because it is so close. Monday, October 24, 2011 General Properties • Average star • Spectral type G2 - O B A F G K M • Only appears so bright because it is so close. • 109 times Earth’s diameter Monday, October 24, 2011 General Properties • Average star • Spectral type G2 - O B A F G K M • Only appears so bright because it is so close. • 109 times Earth’s diameter • 333,000 times Earth’s mass Monday, October 24, 2011 General Properties • Average star • Spectral type G2 - O B A F G K M • Only appears so bright because it is so close. • 109 times Earth’s diameter • 333,000 times Earth’s mass • Consists entirely of gas (av. density = 1.4 g/cm3) Monday, October 24, 2011 General Properties • Average star • Spectral type G2 - O B A F G K M • Only appears so bright because it is so close. • 109 times Earth’s diameter • 333,000 times Earth’s mass • Consists entirely of gas (av. density = 1.4 g/cm3) • Central temperature = 15 million K Monday, October 24, 2011 General Properties • Average star • Spectral type G2 - O B A F G K M • Only appears so bright because it is so close. • 109 times Earth’s diameter • 333,000 times Earth’s mass • Consists entirely of gas (av. density = 1.4 g/cm3) • Central temperature = 15 million K • Surface temperature = 5800 K Monday, October 24, 2011 Very Important Warning: Never look directly at the sun through a telescope or binoculars!!! Monday, October 24, 2011 Very Important Warning: Never look directly at the sun through a telescope or binoculars!!! This can cause permanent eye damage – even blindness. Monday, October 24, 2011 Very Important Warning: Never look directly at the sun through a telescope or binoculars!!! This can cause permanent eye damage – even blindness. Use a projection technique or a special sun viewing filter. Monday, October 24, 2011 The Solar Atmosphere Monday, October 24, 2011 The Solar Atmosphere Only visible during solar eclipses Monday, October 24, 2011 The Solar Atmosphere Only visible during solar eclipses Apparent surface of the sun Monday, October 24, 2011 The Solar Atmosphere Only visible during solar eclipses Apparent surface of the sun Solar interior Monday, October 24, 2011 The Solar Atmosphere Only visible during solar eclipses Apparent surface of the sun Solar interior Monday, October 24, 2011 Temp. incr. inward The Solar Atmosphere Apparent surface of the sun Heat Flow Only visible during solar eclipses Solar interior Monday, October 24, 2011 Temp. incr. inward The Photosphere • Apparent surface layer of the sun Monday, October 24, 2011 The Photosphere • Apparent surface layer of the sun • Depth ≈ 500 km Monday, October 24, 2011 The Photosphere • Apparent surface layer of the sun • Depth ≈ 500 km • Temperature ≈ 5800 oK Monday, October 24, 2011 The Photosphere • Apparent surface layer of the sun • Depth ≈ 500 km • Temperature ≈ 5800 oK • Highly opaque (H- ions) Monday, October 24, 2011 The Photosphere • Apparent surface layer of the sun • Depth ≈ 500 km • Temperature ≈ 5800 oK • Highly opaque (H- ions) • Absorbs and re-emits radiation produced in the sun Monday, October 24, 2011 The Photosphere • Apparent surface layer of the sun • Depth ≈ 500 km • Temperature ≈ 5800 oK • Highly opaque (H- ions) • Absorbs and re-emits radiation produced in the sun The solar corona Monday, October 24, 2011 Energy Transport in the Photosphere Energy generated in the sun’s center must be transported outward. Monday, October 24, 2011 Energy Transport in the Photosphere Energy generated in the sun’s center must be transported outward. Near the photosphere, this happens through Convection: Monday, October 24, 2011 Energy Transport in the Photosphere Energy generated in the sun’s center must be transported outward. Near the photosphere, this happens through Convection: Bubbles of hot gas rising up Monday, October 24, 2011 Energy Transport in the Photosphere Energy generated in the sun’s center must be transported outward. Near the photosphere, this happens through Convection: Cool gas sinking down Monday, October 24, 2011 Bubbles of hot gas rising up Energy Transport in the Photosphere Energy generated in the sun’s center must be transported outward. Near the photosphere, this happens through Convection: Cool gas sinking down ≈ 1000 km Monday, October 24, 2011 Bubbles of hot gas rising up Energy Transport in the Photosphere Energy generated in the sun’s center must be transported outward. Near the photosphere, this happens through Convection: Cool gas sinking down Bubbles of hot gas rising up ≈ 1000 km Bubbles last for ≈ 10 – 20 min Monday, October 24, 2011 Granulation … is the visible consequence of convection. Monday, October 24, 2011 The Chromosphere Monday, October 24, 2011 The Chromosphere • Region of sun’s atmosphere just above the photosphere Monday, October 24, 2011 The Chromosphere • Region of sun’s atmosphere just above the photosphere • Visible, UV, and X-ray lines from highly ionized gases Monday, October 24, 2011 The Chromosphere • Region of sun’s atmosphere just above the photosphere • Visible, UV, and X-ray lines from highly ionized gases Chromospheric structures visible in Hα emission (filtergram) Monday, October 24, 2011 The Chromosphere • Region of sun’s atmosphere just above the photosphere • Visible, UV, and X-ray lines from highly ionized gases • Temperature increases gradually from ≈ 4500 oK to ≈ 10,000 oK, then jumps to ≈ 1 million oK Chromospheric structures visible in Hα emission (filtergram) Monday, October 24, 2011 The Chromosphere • Region of sun’s atmosphere just above the photosphere • Visible, UV, and X-ray lines from highly ionized gases • Temperature increases gradually from ≈ 4500 oK to ≈ 10,000 oK, then jumps to ≈ 1 million oK Transition region Chromospheric structures visible in Hα emission (filtergram) Monday, October 24, 2011 The Chromosphere • Region of sun’s atmosphere just above the photosphere • Visible, UV, and X-ray lines from highly ionized gases • Temperature increases gradually from ≈ 4500 oK to ≈ 10,000 oK, then jumps to ≈ 1 million oK Filaments Transition region Chromospheric structures visible in Hα emission (filtergram) Monday, October 24, 2011 The Layers of the Solar Atmosphere Monday, October 24, 2011 The Layers of the Solar Atmosphere Visible Monday, October 24, 2011 The Layers of the Solar Atmosphere Visible Monday, October 24, 2011 Ultraviolet The Layers of the Solar Atmosphere Visible Monday, October 24, 2011 Sun Spot Regions Ultraviolet The Layers of the Solar Atmosphere Visible Monday, October 24, 2011 Sun Spot Regions Ultraviolet The Layers of the Solar Atmosphere Visible Sun Spot Regions Ultraviolet Coronal activity, seen in visible light Monday, October 24, 2011 The Layers of the Solar Atmosphere Visible Sun Spot Regions Ultraviolet Photosphere Coronal activity, seen in visible light Monday, October 24, 2011 The Layers of the Solar Atmosphere Visible Sun Spot Regions Ultraviolet Photosphere Chromosphere Coronal activity, seen in visible light Monday, October 24, 2011 The Layers of the Solar Atmosphere Visible Sun Spot Regions Ultraviolet Photosphere Corona Chromosphere Coronal activity, seen in visible light Monday, October 24, 2011 The Magnetic Carpet of the Corona • Corona contains very low-density, very hot (1 million oK) gas Monday, October 24, 2011 The Magnetic Carpet of the Corona • Corona contains very low-density, very hot (1 million oK) gas • Coronal gas is heated through motions of magnetic fields anchored in the photosphere below (“magnetic carpet”) Monday, October 24, 2011 The Magnetic Carpet of the Corona • Corona contains very low-density, very hot (1 million oK) gas • Coronal gas is heated through motions of magnetic fields anchored in the photosphere below (“magnetic carpet”) Computer model of the magnetic carpet Monday, October 24, 2011 What effect does the formation of negative hydrogen ions in the sun's photosphere have on solar observations? 1. We can view the sun's interior through special filters set to the wavelength of the absorption lines created by such ions. • Concentrations of such ions form sunspots that allow us to track solar rotation. • It divides the sun's atmosphere into three distinct, easily observable layers. • The extra electron absorbs different wavelength photons making the photosphere opaque. • These ions produce the "diamond ring" effect that is seen during total solar eclipses. Monday, October 24, 2011 This diagram explains the structure of solar granules. Why is the center of a granule brighter than its edges? 1. The surface elevation is higher at the center. 2. The surface elevation is lower at the center. 3. The temperature is higher at the center. 4. The temperature is lower at the center. 5. The surface elevation is lower at the center. Monday, October 24, 2011 The sun’s atmospheric layers are all less dense than its interior. Based on this figure, which layer of the sun is responsible for the absorption lines in the solar spectrum? 1. Corona 2. Chromosphere 3. Photosphere 4. All the layers are responsible. 5. Both corona and chromosphere Monday, October 24, 2011